#include <bits/stdc++.h>
using namespace std;
 
 
int solve(vector<int>& a){
	int n = a.size();
	int totalSum = accumulate(a.begin(),a.end(),0);
	if(totalSum%3!=0)return 0;
	int y = totalSum/3;
	unordered_map<int,int>prefixSum;
	int c=0,sum=0;
	for(int i=0;i<n-1;i++){
		sum += a[i];
		if(sum == 2*y && prefixSum.count(y)!=0){
			c += prefixSum[y];
		}
		prefixSum[sum]++;
	}
	return c;
}
 
int main() {
	int n;
	cin>>n;
	vector<int>a(n);
	for(int i=0;i<n;i++){
		cin>>a[i];
	}
	cout<<solve(a);
	return 0;
}

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NwoxIDIgMCAwIDEgMiAz

7
1 2 0 0 1 2 3